• Object: either a class or an instance, but typically refers to an instance.

• Class: a description of a set of similar objects, the instances. This description typically includes:
  • Instance variables: the names of variables that are assumed to be defined for every subclass or instance of the class.

  • Methods: definitions of messages to which members of the class can respond.

• Instance: an individual member of a class. Typically an instance must be a member of exactly one class. An instance is a data structure that:
  • can be identified as being an object
  • denotes the class to which the object belongs
  • contains values of the instance variables
• Superclass: a class to which a given class belongs. Sometimes a class may have more than one superclass.

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